This application pertains to the art of power drive assemblies and more particularly belt drive assemblies. The invention finds particular application in power drives for wheelchairs in which a pair of power drive assemblies are coordinated or synchronized. Although the preferred embodiment is described in conjunction with power wheelchairs, it is to be appreciated that the invention has broader applications including belt drives between motors and fans, pumps, pulleys, winches, and other rotatably driven apparatus.
Helicopters have utilized a pair of rollers which wrap a drive belt more completely around a driving and/or driven pulley to increase the area of frictional engagement between the belt and pulley. This increased area of engagement reduced belt pulley slippage. Electric wheelchairs have commonly included a pair of electric motors one of which was connected by a left belt drive with the left rear driving wheel and the other of which was connected with a right belt drive to the right rear driving wheel. Each motor was connected by a gearbox with a pulley disposed in the same plane as a pulley on its associated rear wheel. A V-belt extended around the drive pulley and the rear wheel pulley. Each motor, its associated gearbox and pulley were mounted within the wheelchair in a manner which allowed them to be moved fore and aft relative to the rear wheel such that the tension on the V-belt could be adjusted. Typically, 55 pounds of tension were required on the belt to transmit 150 inch pounds of torque without slippage.
One of the problems with the prior art high tension wheelchair drive assemblies was that the belts tended to wear or stretch which induced slippage relative to the pulleys. Uneven slippage between the left and right drive assemblies would cause the wheelchair to undergo unexpected and undesired turning motions.
Another of the problems with maintaining the high tension on the belts was that the pulleys were overloaded. The overloading shortened belt life and increased the wear on the bearings associated with the gearbox and pulleys. Still another problem resulting from the high belt tension of the prior art wheelchairs was that the batteries drained relatively rapidly. A pair of series connected 12-volt, 45 ampere-hour related batteries, as commonly used in wheelchairs, provide a driving range of about 15-16 miles per charge. The battery drain was attributable not only to energy to move the chair but to the power required to overcome frictional and other loads attributable to the high belt tension.